When the Spaniard signed for McLaren, he did so expecting to add to his haul of drivers' championship titles.

This dream soon became a nightmare due to the stellar performances of his McLaren team-mate Lewis Hamilton.

But for the Briton's lack of experience and bad luck, particularly during the German and Chinese Grand Prix, it seems unlikely that a decision on the drivers' championship would have to depend on the final race of the season.

Alonso's task in defending his drivers' championship title has not been made easier by the glacial atmosphere within the McLaren team, particularly from the Hungarian Grand Prix weekend onwards and in the wake of the Formula One spy scandal enquiry by the FIA. The twotimes world champion also has to contend with being the subject of increasing speculation regarding his Formula One future.

Alonso must win today's race if he is to have any realistic chance of retaining his title. Even at that, he has to hope that Hamilton and Raikkonen fail to secure the necessary points to surpass his total.

Given the unpredictability inherent in the sport, as evidenced by Friday's tyre controversy, this scenario might well unfold, particularly if Ferrari's Felipe Massa proves to be the deciding factor in the race and the drivers' championship. However, both Alonso and Raikkonen will be acutely aware that the drivers' championship is Hamilton's to lose, rather than theirs to win.

For Alonso, the result of today's Brazilian Grand Prix could substantially affect his future Formula One career.

Notwithstanding the jocular interaction between the Spaniard and team-mate Hamilton, at Thursday's press conference, it is virtually certain that Alonso's career with McLaren will end this weekend, whatever the outcome of the race. Having ruled out taking a sabbatical year away from the Formula One arena, Alonso will be looking to Renault or Toyota to provide him with a raceberth for 2008 and beyond.

A return to Renault for 2008 would be an ideal re-set of his Formula One career.

Renault supremo Flavio Briatore has made no secret of his willingness to see Alonso return to the French team, where he would renew a highly successful working relationship with the Italian, which yielded two drivers' championships for the Spaniard in 2005 and 2006 and which could see the French outfit return to a championship-winning mode.

However, if the prospect of a return to Renault does not materialise, it could be as a consequence of the rumoured multi-million euro contract on offer by Toyota. A collaboration between Alonso and Toyota could prove extremely fruitful, particularly if the Spaniard's car-development acumen is fully utilised.

Although Hamilton, mathematically at least, will start as favourite today, Alonso's former, and potential, employer Flavio Briatore contends that the Spaniard's experience will propel him to the title. Should this be the outcome, Alonso would bring to another team all the advantages that being champion would entail.

While Alonso's McLaren career could yet end on the ultimate high note, he has expressed the feeling that he did not receive from McLaren the primacy he expected, a view echoed by four-times world champion Alain Prost, in an interview with Italian magazine Autosprint, during which the Frenchman contends that Alonso should have been given the role of team-leader.

However, McLaren's encouragement of its drivers to race each other enabled Hamilton to exhibit his brilliance, as opposed to filling a secondary, supporting role to Alonso. Hamilton is the first team-mate who has presented Alonso with a significant challenge. The Briton's performances at McLaren, in his maiden Formula One year, have raised fundamental questions about Alonso's true abilities.

Perhaps irrespective of the final 2007 championship standings, and regardless of his Formula one future, it is not unreasonable to wonder if Alonso's Formula One stock has been significantly devalued.